Patch "Btrfs: fix delalloc accounting leak caused by u32 overflow" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

Btrfs: fix delalloc accounting leak caused by u32 overflow

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
btrfs-fix-delalloc-accounting-leak-caused-by-u32-overflow.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Omar Sandoval <[email protected]>
Date: Fri, 2 Jun 2017 01:20:01 -0700
Subject: Btrfs: fix delalloc accounting leak caused by u32 overflow

From: Omar Sandoval <[email protected]>

commit 70e7af244f24c94604ef6eca32ad297632018583 upstream.

btrfs_calc_trans_metadata_size() does an unsigned 32-bit multiplication, which can overflow if num_items >= 4 GB / (nodesize * BTRFS_MAX_LEVEL * 2). For a nodesize of 16kB, this overflow happens at 16k items. Usually, num_items is a small constant passed to btrfs_start_transaction(), but we also use btrfs_calc_trans_metadata_size() for metadata reservations for extent items in btrfs_delalloc_{reserve,release}_metadata().

In drop_outstanding_extents(), num_items is calculated as inode->reserved_extents - inode->outstanding_extents. The difference between these two counters is usually small, but if many delalloc extents are reserved and then the outstanding extents are merged in btrfs_merge_extent_hook(), the difference can become large enough to overflow in btrfs_calc_trans_metadata_size().

The overflow manifests itself as a leak of a multiple of 4 GB in delalloc_block_rsv and the metadata bytes_may_use counter. This in turn can cause early ENOSPC errors. Additionally, these WARN_ONs in extent-tree.c will be hit when unmounting:

    WARN_ON(fs_info->delalloc_block_rsv.size > 0);
    WARN_ON(fs_info->delalloc_block_rsv.reserved > 0);
    WARN_ON(space_info->bytes_pinned > 0 ||
            space_info->bytes_reserved > 0 ||
            space_info->bytes_may_use > 0);

Fix it by casting nodesize to a u64 so that btrfs_calc_trans_metadata_size() does a full 64-bit multiplication. While we're here, do the same in btrfs_calc_trunc_metadata_size(); this can't overflow with any existing uses, but it's better to be safe here than have another hard-to-debug problem later on.

---
 fs/btrfs/ctree.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -2547,7 +2547,7 @@ u64 btrfs_csum_bytes_to_leaves(struct bt
 static inline u64 btrfs_calc_trans_metadata_size(struct btrfs_fs_info *fs_info,
 						 unsigned num_items)
 {
-	return fs_info->nodesize * BTRFS_MAX_LEVEL * 2 * num_items;
+	return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * 2 * num_items;
 }
 
 /*

@@ -2557,7 +2557,7 @@ static inline u64 btrfs_calc_trans_metad
 static inline u64 btrfs_calc_trunc_metadata_size(struct btrfs_fs_info *fs_info,
 						 unsigned num_items)
 {
-	return fs_info->nodesize * BTRFS_MAX_LEVEL * num_items;
+	return (u64)fs_info->nodesize * BTRFS_MAX_LEVEL * num_items;
 }
 
 int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans,

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/btrfs-fix-delalloc-accounting-leak-caused-by-u32-overflow.patch